Summary For men who have sex with men (MSM) who engage in exchange sex (i.e., offering sex in exchange for money, drugs, shelter, or goods), gay hookup apps and websites have become a common venue for meeting clients. Further, it has been argued that these new technologies have made male sex work safer, more anonymous and normalized in the gay community, thus likely diversifying and expanding the number of MSM who participate in exchange sex. However, this population of MSM is currently not well characterized or understood from a public health perspective. The goal of the study is to investigate a very under-studied population?MSM who use hookup apps/websites to find clients for exchange sex. The proposed research will be extremely valuable in better characterizing this population and its sexual practices, risk behavior, and risk reduction strategies. We will also examine participants? HIV and STI testing behavior and their attitudes toward PrEP. Because exchange sex is most prevalent among Black, Hispanic, and White MSM ages 18?45, we will conduct in-depth qualitative interviews with an ethnically diverse sample of 180 HIV-uninfected MSM (60 Black, 60 Latino, and 60 White participants, half of them ages 18?29 and half 30?45). To better understand the factors associated with sexual risk taking among men who engage in exchange sex, half of the men in each age and racial/ethnic group will have only had protected sex (either consistent condom use or consistent use of PrEP) and half will have had unprotected anal sex (condomless sex without taking PrEP) with their clients in the prior three months. The study aims are: 1. To investigate participants? pathways into exchange sex, how they use hookup apps/websites to find and negotiate with clients, and how they evaluate the worth of different acts and partners. 2. To investigate the heuristics and risk-reduction strategies?including PrEP and HIV and STI testing?participants use to try to manage the risks of becoming HIV infected and their reasons for their choices. 3. To investigate what types of HIV/STI and sexual health interventions participants would find useful, how they would like these delivered, and then, use findings to develop a provisional intervention to reduce sexual-risk behavior among MSM who use hookup apps/websites to find clients for exchange sex.